Preheat oven to 400. Line two baking sheets with parchment paper.
Arrange bacon on one baking sheet, in a single layer.
Halve tomatoes. Add to a medium bowl. Add olive oil, salt, and pepper to bowl. Toss to coat. Arrange tomatoes in a single layer on the second baking sheet.
Add both sheets to oven. Bake 5 minutes. Trade positions and bake an additional 7 minutes.
While bacon and tomatoes are baking, slice avocado. Toast bread.
When bacon and tomatoes are cooked, build your sandwiches with bacon, tomatoes, and avocados. Serve immediately.