Preheat the oven to 180 C. Chop the tomatoes into bite-sized pieces. Toss with 1 tsp olive oil and salt. Lay them out without overlaps on a baking tray and roast for 35-40 mins. Set aside.
Cook the pasta according to packet instructions. Reserve ½ cup of the cooking liquid, then drain and set aside.
Pesto: add the spinach to a pan and move it around until it just starts to wilt - about 3 mins (same treatment for frozen spinach). Squeeze out the excess moisture in a colander or with your hands.
Add the spinach to a blender jar along with green chillies, cashews, basil, garlic, Parmesan, and salt. Coarsely blitz, stopping to scrape down the sides a few times.
Once it’s a coarse paste, add lemon juice and olive oil and blitz again to get it to the consistency you like. If it appears too dry, add a touch of water to loosen. Taste and adjust seasoning/spice levels. Blend in a bit more chilli at this stage if you like.
Toss the pasta with the pesto, tomatoes, and a few basil leaves. If it feels too dry, add a bit of the reserved cooking liquid to loosen. Serve immediately.