Remove the stem from the tomato and slice it horizontally into 1cm thick pieces. Mince the garlic.

Boil water in a pot, add salt (not listed in ingredients) and spaghetti, and cook according to package instructions. Drain and reserve 2 tbsp of pasta cooking water.

Heat 1/2 tbsp olive oil in a frying pan over low heat. Add garlic and red chili, sauté until fragrant. Add tomato slices, season with salt and pepper, and cook over medium heat for 2 minutes on one side and 1 minute on the other. Remove the grilled tomatoes.

In a bowl, mix the cooked spaghetti, reserved pasta water, remaining olive oil (1 1/2 tbsp), and mozzarella cheese. Adjust seasoning with salt and pepper.