Preheat the oven to 400°F. Place the cherry tomatoes on a small baking sheet, drizzle with olive oil, and season with salt and pepper. Roast for 15 to 20 minutes until blistered, burst, and slightly caramelized. Set aside.
Cook the pasta in a large pot of generously salted boiling water according to package directions until al dente. Reserve 1/2 cup of pasta water before draining.
Return the drained pasta to the warm pot over low heat. Add the entire jar of pesto and the olive brine and toss until every piece of pasta is evenly coated. Add a splash of the reserved pasta water to loosen the sauce if needed.
Add the fresh spinach leaves and toss until wilted into the warm pasta.
Fold in the roasted tomatoes and fresh diced tomatoes gently.
Taste and adjust salt and pepper as needed. Serve immediately.