Halve and core the 2 avocados. Scoop the pulp into a bowl and mash with a fork until creamy. Stir in the cream cheese and 1 pressed garlic clove. Season with lemon juice, salt, and pepper. Finely dice the onion and tomato, add to the guacamole, and season again if necessary.
Cut the chicken breast fillets in half. Cut a horizontal pocket into the cut side of each piece, being careful not to cut all the way through. Stuff each pocket with guacamole. Secure the opening with a small skewer. Wrap each filled chicken piece with bacon.
Heat a pan over medium-high heat. Sear the bacon-wrapped chicken pieces 3-4 minutes per side until the bacon is browned. Transfer to an oven preheated to 200°C (400°F). Bake for 20 minutes until the thickest part reaches 74°C (165°F) internal temperature.
Serve the chicken with the remaining guacamole as a dip.