Cook the pasta: Bring a large pot of salted water to a boil. Cook the pasta according to package directions until al dente. Drain well and spread on a sheet pan to cool slightly.
Drizzle with a little olive oil to prevent sticking if you like.
Crisp the bacon: While the pasta cooks, fry the bacon in a skillet over medium heat until crispy. Transfer to a paper towel–lined plate, then crumble once cooled.
Prep the produce: Halve the tomatoes, dice the cucumber, and slice the red onion. Dice the avocados last and toss them with the lemon juice to slow browning.
Make the dressing: In a large bowl, whisk together ranch dressing, mayonnaise or Greek yogurt, garlic powder, a pinch of salt, and black pepper.
Adjust to taste.
Combine: Add the cooled pasta to the bowl with the dressing and toss to coat. Gently fold in bacon, tomatoes, cucumber, red onion, cheese (if using), and herbs.
Add avocado: Fold in the avocado carefully so it stays chunky. Taste and season with more salt, pepper, or lemon juice as needed.
Chill or serve: You can serve right away or cover and chill for 30 minutes to let the flavors meld.
If chilling longer than an hour, hold the avocado and half the bacon back and add just before serving for best texture.