Preheat your oven to 375°F (190°C).
Heat olive oil in a large pan.
Add onions and garlic to the pan.
Cook for 3-4 minutes until softened.
Add carrots and cook for 5 minutes.
Add broccoli and bell peppers next.
Season vegetables with salt and pepper.
Cook everything for 8-10 minutes total.
Transfer vegetables to your baking dish.
Mix flour and cold butter together.
Rub mixture until it resembles breadcrumbs.
Add cheese, breadcrumbs, and herbs.
Sprinkle crumble over the cooked vegetables.
Bake for 25-30 minutes until golden.
Let cool for 5 minutes before serving.