Peel onion, dice and fry in a pan in hot oil. Add rice and let glaze over while stirring. Pour in a little broth, cook while stirring until it evaporates and is absorbed. Pour in wine, likewise continue to stir and allow to evaporate and absorb. Continue to add broth and wine in this manner and cook until rice is al dente, about 30 minutes, stirring frequently.
Remove rice from the heat and stir butter into the rice. Blanch tomatoes in boiling hot water, peel, quarter, remove seeds and cut into strips. Cut cooked asparagus into large pieces. Rinse arugula and chop. Gently stir tomatoes, asparagus and arugula into the rice. Sprinkle with grated Parmesan cheese and season with salt and pepper and serve.