No proportions have been measured. It's mostly guesswork, but here are the ingredients:
Very finely chopped onion
Dijon mustard (or whatever mustard is on hand)
Bread crumbs or cracker crumbs, finely crumbled
Salt and pepper
1 or 2 eggs, beaten with fork a few times
Little BBQ sauce (optional)
This can really stretch some ground beef to feed a lot more people. Mix everything together by hand, adding enough of the wetter ingredients to make it kneadable. Get your hands in there and squish it all together really well till well incorporated, and form it into a loaf or loaves. Or form one loaf and set aside the remaining portion as the filling for stuffed green bell peppers. Bake meatloaf in loaf pan or oval casserole 350 F till middle is firm and top is nicely browned. I put tin foil over mine while baking and then take it off as it gets done and let it brown up the last 10 minutes or so.
If you want a topping, it can be ketchup or ketchup mixed with a bit of brown sugar and pepper and spread over top before cooking.
You can throw about anything into a meatloaf, even diced leftover veggies as long as you have a good proportion of meat and bread crumbs/oatmeal and spices in there, and the egg(s) as a binder to keep it from falling apart.
For stuffed green peppers, clean, de-seed, and cut in half 2 or 3 bell peppers (any color) and fill each with a portion of the meatloaf mix.
NOTE: if you want to make stuffed peppers and NOT separate meatloaf, you CAN substitute cooked rice for the oatmeal and some of the breadcrumbs. But no worries if you don't have it on hand.
Place in a casserole, cover with tin foil, and bake 350 till done through. You might want to take the foil off the last few minutes to let the tops brown up nicely.
If you like you can pour spaghetti sauce over all the stuffed peppers before baking, and top with cheese and let it melt on top of them just before finished. Or dab a little tomato sauce and some garlic powder on each before baking.