Preheat the oven to 400°F (200°C). Arrange the mini pizza bases on a baking sheet lined with parchment paper. Gather all toppings and prepare a workspace for assembling.
Heat olive oil in a skillet over medium heat. Add chopped onions and sauté until translucent and fragrant, about 3 minutes. Add chopped bell peppers and cook until slightly softened, about 4 minutes. Turn off heat and let cool slightly.
Spread a thin layer of cooked vegetables evenly over each mini pizza base using a spoon or spatula. Sprinkle dried oregano, salt, and pepper over the toppings for flavor.
Generously sprinkle shredded mozzarella cheese over the vegetable toppings on each pizza base. Ensure an even coverage to melt uniformly during baking.
Bake in the preheated oven for 12-15 minutes, or until the cheese is melted and bubbly, and the edges of the mini bases are golden brown. Watch for visual signs of doneness and if needed, rotate the baking sheet for even browning.
Remove from oven and let cool for a few minutes. Serve warm, optionally garnished with fresh herbs or additional vegetables.