Peel the tomatoes (if using fresh) and cut them into fourths. Place the tomatoes, peppers, onion, garlic, and salt into a blender and process until smooth.
Allow everything to boil gently (not violently, which would cause the meatballs to fall apart), uncovered, for about 30 minutes, until the meatballs are cooked through and the sauce has thickened somewhat to the consistency you desire.
Meatballs in Chipotle Sauce (Albóndigas en salsa de chipotle) https://comboplate.net/meatballs-in-chipotle/