In a medium bowl, whisk to combine eggs, milk, salt, onion, vegetable, and 1/2 cup cheese.
Lay peppers in a lightly greased baking dish (whatever size works- you want them to be a little snug so they don’t move and spill over). Divide your egg mixture between your peppers and sprinkle with remaining cheese. Cover with foil and bake for 40-45 minutes, until eggs are set.
Or, Line slow cooker with tin foil. Place peppers inside and fill. Cook on low for 3-4 hours or until eggs are set.