Heirloom Tomato Bake

butter (plus more to butter your baking dish)

bread, finely diced (ciabatta, sourdough, rosemary loaf, olive loaf, rye, gluten-free, whatever you like!)

green bell peppers, finely diced

yellow onion, finely diced

large heirloom tomatoes (I like alternating colors!)

mozzarella cheese, shredded

parmesan cheese, as desired

salt and pepper

basil, thinly sliced