Caramelised onion frittata with roasted garlic tomatoes

Ingredients (4 servings): 6 tomatoes, halved lengthways 2 garlic cloves, thinly sliced lengthways Olive oil spray 125g (½ cup) light sour cream 2 teaspoons chopped fresh dill 60ml (¼ cup) olive oil 2 brown onions, halved, thinly sliced 1 tablespoon brown sugar 6 eggs, lightly whisked 50g baby rocket leaves 1 tablespoon balsamic vinegar  …