In a medium bowl, whisk together the pesto, lemon juice, olive oil and salt until smooth.
Meanwhile, bring a large pot of salted water to a rolling boil.
Add the refrigerated cheese tortellini and cook according to package instructions until just cooked, usually about 2-3 minutes.
Drain the tortellini well and add to a large bowl. Immediately–while the tortellini is still warm–pour over ⅓ cup of the pesto dressing. Allow the tortellini to sit, cool, and absorb the dressing, about 10 minutes.
Add the tomatoes, spinach, and remaining dressing, tossing to combine. Add the basil, and toss again.
