In a medium bowl, whisk together the pesto, freshly squeezed lemon juice, extra virgin olive oil, salt, and red pepper flakes until well combined and emulsified. The acidity from the lemon juice will help balance the richness of the pesto and oil, creating a bright, cohesive dressing. Set aside while you prepare the pasta.

Bring a large pot of salted water to a rolling boil over high heat. Add the cheese tortellini and cook for 2-3 minutes, or according to package directions—the pasta should be just tender but not mushy, as it will continue to soften slightly as it cools and absorbs the dressing. Drain the tortellini in a colander, shaking gently to remove excess water.

Transfer the warm tortellini to a large serving bowl and immediately pour about 1/3 of the pesto dressing over the pasta. Gently toss to coat evenly, then let it sit for about 10 minutes at room temperature. I find this resting time allows the warm pasta to absorb the dressing flavors more deeply, which creates much better flavor throughout the salad. During this time, prepare the remaining ingredients.

While the pasta absorbs the dressing, halve the cherry tomatoes, roughly chop the baby spinach into 1/2-inch ribbons, and cut the fresh basil leaves into thin chiffonade (thin ribbon-like cuts). Having these ready will make final assembly quick and easy, and the spinach will retain better texture if added just before serving rather than sitting in the warm dressing for too long.

Add the sliced cherry tomatoes, chopped spinach, fresh basil chiffonade, and toasted pine nuts to the bowl with the dressed pasta. Pour the remaining pesto dressing over everything and toss gently but thoroughly until all ingredients are evenly coated and combined. I like to use a light hand when tossing to keep the delicate pasta intact and prevent the spinach from breaking down too much. Taste and adjust seasoning if needed, then serve immediately or chill until ready to serve.