Bring a large pot of lightly salted water to a boil. Cook spaghetti in the boiling water, stirring occasionally, until tender yet firm to the bite, about 12 minutes. Drain and keep warm.
Bring a saucepan of water to a boil while spaghetti is cooking. Cut a cross into the bottom of each tomato and place them in the boiling water for 1 minute. Remove with a slotted spoon and immediately rinse under cold water. Peel, remove central core, and chop pulp.
Heat olive oil in a skillet over medium heat and cook onion until soft and translucent, about 5 minutes. Add garlic and cook until fragrant, about 30 seconds. Add zucchini and cook, stirring occasionally, until softened, about 5 minutes. Season with herbes de Provence, salt, and pepper. Add tomatoes and cream and bring to a boil. Mix in basil. Stir in feta; cook until warmed through but sauce is not boiling, about 1 minute. Stir in drained spaghetti.