Cook the pasta. Boil in salted water until just al dente. Drain and rinse under cool water to stop the cooking. Shake off excess water well.
Season and cook the beef. Warm a skillet over medium-high heat.
Add a touch of oil if your beef is very lean. Brown the beef, breaking it up. Sprinkle with chili powder, cumin, smoked paprika, salt, and pepper.
Cook until no pink remains and any moisture cooks off. Let it cool slightly.
Mix the dressing. In a bowl, whisk Greek yogurt, mayo, BBQ sauce, buttermilk, lime juice, smoked paprika, garlic powder, onion powder, pepper, and salt. Adjust thickness with a splash more milk if needed.
Taste and tweak salt or BBQ sauce.
Prep the veggies. Halve tomatoes, dice onion and bell pepper, chop cilantro, and measure corn and black beans. If using frozen corn, thaw it. If using fresh, a quick sear in a dry pan brings out sweetness.
Toss it all together. In a large mixing bowl, add pasta, warm-but-not-hot beef, beans, corn, tomatoes, onion, bell pepper, and cilantro.
Pour in most of the dressing and toss until everything is lightly coated.
Finish and chill. Fold in cheese if using. Cover and refrigerate 20–30 minutes so flavors settle. Right before serving, add avocado and the remaining dressing to taste.
Season and serve. Add a pinch of salt, extra BBQ sauce, or a squeeze of lime if it needs a lift.
Serve cold or at cool room temperature.