Step 1Place baby tomatoes in a roasting dish and spray with olive oil. Place under a hot grill for 10 minutes until blistered. Remove from oven and set aside.
Step 2Cook spaghetti in a saucepan of boiling water, according to packet instructions. Drain, reserving a little cooking water in a cup, and return pasta to pan.
Step 3Meanwhile, spray a large non-stick frying pan with olive oil and set over medium-high heat. Cook mushrooms, stirring, for 3–4 minutes, or until softened. Add pesto with reserved pasta water, and mix gently to heat through and create a sauce.
Step 4Add mushrooms and pesto to spaghetti with roasted tomatoes, baby spinach, lemon zest and juice, and half of the parmesan. Divide among 4 serving plates and top with remaining cheese.