Cook the spaghetti: Bring a large pot of salted water to a boil. Cook spaghetti until just al dente.
Reserve 1/2 cup pasta water, drain, and set aside.
Sauté aromatics: In a large skillet, heat olive oil over medium heat. Add onion and bell pepper. Cook 4–5 minutes, stirring, until softened.
Add garlic and cook 30 seconds until fragrant.
Brown the chicken: Add ground chicken to the skillet. Break it up with a spoon and cook until no longer pink, about 5–6 minutes. Sprinkle in the taco spice blend and stir to coat.
Build the sauce: Stir in tomato paste, then add diced tomatoes with their juices, black beans, and 3/4 cup chicken broth.
If using corn, add it now. Simmer 5–7 minutes to thicken slightly.
Make it creamy: Reduce heat to low. Stir in Greek yogurt or light cream cheese until smooth.
If the sauce is too thick, splash in more broth or a bit of reserved pasta water.
Toss with pasta: Add cooked spaghetti to the skillet. Toss until well coated. Add reserved pasta water as needed to loosen and help the sauce cling.
Finish with freshness: Stir in cilantro, lime zest, and a squeeze of lime juice.
Taste and adjust salt, pepper, and heat.
Optional toppings: Sprinkle with a little reduced-fat cheese to melt. Top with avocado slices and extra cilantro.
Serve: Plate hot and enjoy. A crisp side salad or roasted veggies make a great pairing.