Preheat oven to 350 degrees. Line a rimmed baking sheet with foil for easy cleanup. Place tenderloin on prepared baking sheet. Brush with olive oil and sprinkle with salt and pepper.
Bake for 45 to 50 minutes or until an internal thermometer reaches 165 degrees. Remove from oven, tent with foil, and let rest for 5 to 10 minutes before slicing.
Meanwhile, preheat a large skillet over medium heat (about 375 degrees). Arrange the bacon in a single layer, working in batches as necessary, and fry until crisp. Break slices in half.
To make the pesto mayonnaise, combine pesto and mayonnaise in a small bowl and stir to combine. Cover and chill while the tenderloin is baking.
To make the sandwiches, toast the Texas toast. Spread 1 heaping tablespoon of pesto mayonnaise on half of the toast. Top each with two slices tomato and sprinkle with salt and pepper.
Continue building the sandwiches by layering lettuce, turkey, turkey bacon, and avocado on each. Top with the remaining toast slices, cut in half, and serve.
Turkey Tenderloins are often sold in a 2-pack (24 ounces total). You could bake both to double the recipe (or eat it on its own) or freeze one for later.
To grill the turkey tenderloin, preheat grill over medium heat and place tenderloins directly on grate. Grill, turning occasionally, until meat thermometer inserted into thickest portion of the meat reaches 165°F, approximately 45-50 minutes. Remove from heat, cover and let rest 5-10 minutes before slicing.
To cook the turkey tenderloin in a slow cooker, add ½ cup water with the tenderloin(s) and cover with lid. Cook 2 to 3 hours on HIGH or 3 to 4 hours on LOW AND until internal temperature reaches 165°F.
To bake the turkey bacon, preheat oven to 375°F. Place desired number slices on pan. Bake 8-12 minutes or to desired crispness, no turning is necessary.
To broil the turkey bacon, preheat broiler. Place desired number of bacon slices on rack or broiler pan. Broil bacon, 6 inches from heat source for 5 minutes turning every 2 minutes to desired crispness.