Whisk together the homemade ranch dressing and BBQ sauce in a medium bowl
Place chicken in a large, resealable plastic bag. Pour half the BBQ mixture over the chicken (reserve remaining mixture)
Refrigerate chicken for 30 minutes
Preheat grill to medium-high heat
Remove chicken from bag and discard marinade
Place chicken on grill and cook for 5-7 minutes. Flip and cook for 5 minutes more or until chicken registers 165 degrees with a meat thermometer. Let chicken rest for 5 minutes
Toss zucchini and bell pepper with olive oil. Season with salt and pepper.
Place them in a grill basket and cook until softened and cooked through, ~5-7 minutes
Thinly slice chicken
Toss the grilled vegetables with corn in a large bowl. Top with chicken + diced avocado
Drizzle on remaining barbecue ranch sauce