Carve crosswise the tomatoes, blanch in salted water, peel and dice.
Heat the olive oil in a ovenproof pan. Add the onions, garlic, and the vegetables and sauté briefly. Add the rice and sauté but avoid that it gets brown. Preheat the oven to 200° C convection.
Add the vegetable stock and bring to a boil. Season with salt, pepper and saffron. Place the pan in the oven and let the paella cook for about 15-20 minutes. Then serve.