Combine tomatoes, bell pepper, jalapeño, onion, garlic and bread in a blender. Add 1 cup juice and pulse until chunky. Whisk in vinegar and oil and season with salt and pepper. Thin with additional juice, 2 Tbsp. at a time, until mixture reaches desired consistency. Cover and chill at least 2 hours or overnight.
Check seasoning, adjust if desired, and serve cold, topped with scallions and avocado, if using.