Rinse the zucchinis, cut into quarters lengthwise and slice thinly. Peel and mince the garlic. Heat the olive oil in a large pan and sauté the zucchini, garlic and chopped thyme for about 5 minutes, until browned. Season with salt and pepper.
Whisk the eggs and whipping cream together until smooth. Season with salt and pepper and pour over the zucchini mixture. Reduce heat to low, cover and cook for 8-10 minutes. Carefully flip the frittata onto a plate and slide back into the pan to cook the other side. Sprinkle with Parmesan cheese, cover and cook for another 3-5 minutes, until the bottom is golden brown and the cheese has melted.
Cut the frittata into wedges, place on a serving platter and garnish with sliced tomatoes and fresh basil.