Step 1 Preheat oven to 180°C. Cook pasta according to packet instructions. Drain well.
Step 2 Meanwhile, spray a large frying pan with oil and place over medium heat. Add onion, carrot and celery and cook, stirring, for 6–7 minutes, until soft. Add mince, breaking it up with a wooden spoon, and cook for 5–6 minutes, until browned. Add tomato paste, stirring for 1–2 minutes, then add tomatoes and 1/4 cup water. Stir to combine and simmer for 5 minutes.
Step 3 Add pasta to mince mixture and stir to combine. Spray a 2-litre ovenproof baking dish with oil and transfer pasta mixture to dish. Smooth the top with the back of a spoon.
Step 4 Blanch zucchini in a large saucepan of boiling water for 1–2 minutes, then plunge into a bowl of cold water. Drain well. Layer zucchini slices, slightly overlapping, over pasta mixture. Then layer tomato over zucchini. Dot ricotta over tomatoes and season with ground black pepper. Bake for 20 minutes, placing under a hot grill for the last 5 minutes of cooking, until top is browned. Serve with steamed green vegies.