Season the chicken: Pat the chicken dry and season with salt and pepper. If you like a little kick, add a pinch of red pepper flakes.
Sear the chicken: Heat 1 tablespoon olive oil in a large, deep skillet over medium-high heat.
Add the chicken in an even layer and cook, stirring once or twice, until browned and cooked through, 5–7 minutes. Transfer to a plate.
Sauté aromatics: In the same skillet, add the remaining tablespoon of olive oil. Add onion and a pinch of salt.
Cook until translucent, 3–4 minutes. Stir in garlic and cook 30 seconds, until fragrant.
Simmer tortellini: Pour in the chicken broth and bring to a simmer. Add tortellini, stirring to coat.
Cover and cook over medium heat according to package time, usually 3–5 minutes, until almost tender. If the pan looks dry, splash in a bit more broth or water.
Add asparagus and tomatoes: Stir in asparagus and cherry tomatoes. Cover again and cook 2–3 minutes, until the asparagus is crisp-tender and tomatoes start to soften.
Make it saucy: Reduce heat to low.
Stir in the cream (if using), pesto, and Parmesan. Return the chicken and any juices to the pan. Gently toss until everything is coated and heated through, 1–2 minutes.
Add lemon juice and zest.
Adjust and serve: Taste and season with more salt, pepper, or pesto. For extra brightness, add another squeeze of lemon. Garnish with fresh basil and more Parmesan.
Serve hot.