To par-cook bacon, lay slices on a sheet pan and bake in a preheated 400 degree F oven for about 10 minutes until half-cooked. Remove and reserve.
Working on a sheet pan, coat the chicken breast with olive oil and minced garlic. Sprinkle lightly with salt and pepper. Next, wrap 2 pieces of par-cooked bacon strips criss-cross around each piece of chicken, forming an "x" pattern in the center. Sprinkle with the diced onion and place a thick slice of Roma tomato and a couple sprigs of fresh thyme in the center of each breast, tucked in behind the bacon.
Arrange chicken a little apart from each other on the sheet pan and bake until the chicken is completely cooked and reaches an internal temperature of 165 degrees F, about 30 minutes.