Ehhh, I'm not on a device where I can copy/paste in, so I'm working from memory here, and I'm fucking old.
1 egg per pound of meat.
Meat should be fairly low fat, no more than 15%, and that's stretching things.
Beef should be no less than 75% of the meat, with ground pork being a good choice for the rest, and ground chicken being a good choice to mix with pork about 50/50 for the rest.
Seasonings: salt and pepper to taste. Minced or shredded onion, app 1/4 cup up to 3 lbs of meat, or to taste. One clove of garlic finely minced for up to 3 lbs. Both onion and garlic can be freely reduced, but you shouldn't go over that amount. You can replace with granulated versions, but you'll need to reduce the "filler".
The filler would be about 1/8 cup of panko and about the same of coarsely ground oats. You don't want oat flour, you want some visible particles. Why the oat? Texture. It gives a mouth feel that's better than going with only breadcrumbs, and when you're using ground pork, it evens things out in that regard.
You can "go further" if you're trying to stretch a smaller amount of meat and dice up some peppers (sweet red bell are bomb).
If you like mushrooms, dice about a half cup. Fairly fine, but not fully minced. Texture + flavor. Yeah, you can do the powdered soup for the taste, but finely diced real are better. If you don't like them, leave them out, but you'd be better off just mocking mincing them super fine for the taste. It really does boost the beef a lot.
A dash to three dashes of Worcestershire sauce. You can add more if you're skipping shrooms, but add a touch extra breadcrumbs.
Mix by hand until the meat and ingredients are evenly distributed, but avoid mashing the meat. You don't want to apply much pressure until it's mixed well, and then only to shape it.
Shape it? Wtf is this guy on about? No loaf pans, no baking pans. You shape the loaf on a roasting pan with a drip tray. This builds a crust on the exterior, and that Maillard reaction brings flavor.
350ish, time to vary by size, but until thermometer comes out around 140. There will be carryover cooking. Expect about 45 minutes total though.
Once it's in the oven, mix up your topping if you want one. Plain ketchup is okay. Bbq sauces work. In a pinch, ketchup with a dash of Worcestershire is decent. Or you can get fancy. Ketchup is a good starter base. Soy sauce, some molasses or brown sugar, paprika, pepper, garlic powder and a few dashes of Worcestershire is pretty good without trying to build from tomato sauce (which is more hassle than its worth). Key is to get some umami in there, and let any salt come from that. You don't want salty topping.
You would apply a good coating of that to the entire loaf exterior about a half hour into cooking. You want it to have time to caramelize some. You'll need about a cup to a cup and a half total for a 3lb loaf, depending. You'll have some extra, but it's nice to have for leftovers.
When you pull it, let it rest at least 5 minutes. It makes a difference in taste, texture, and juiciness.
Like I said, I'm pulling from memory, the written version has better measurements per pound of meat. But that's the basic idea. You leverage seasonings, umami, and let time & temp work on the exterior. The inside will be slightly "meatier" in texture than a classic meatloaf, but in a good way; but it won't be a big hamburger.
You gotta know your oven though. If it runs much high or low, take that into account. You'd be better off going high than low, since that exterior needs the 350-400 temp range for good crust. Going a bit higher to keep it from going under as the thermostat works is better than letting it dip.