Prepare the vegetables - peel and chop the onion, deseed and chop the pepper and drain the sweetcorn.
Cook the spaghetti following pack instructions.
Meanwhile, melt 10g butter in a frying pan and gently cook the onion for 2-3 minutes until starting to soften. Add the yellow pepper and cook for 2-3 minutes more. Add the sweetcorn, stir until well combined then turn off the heat.
Once the spaghetti is cooked, reserve 3 Tablespoons of the cooking water then drain.
Add the spaghetti back to the pan with the remaining butter, reserved water and a little salt and pepper to taste. Toss together and cook over a low heat until the butter has melted.
Add the vegetables and stir in. Sprinkle in the grated cheddar, stir to combine then leave to cool before packing in a lunch box for your picnic.