Wash the tomatoes and slice them. Cut the mozzarella into slices.
Rinse the chicken breast fillets, pat dry, and cut into slices. Season with salt and pepper. Heat fat in a pan over medium-high heat and sear the chicken 2-3 minutes per side until golden brown.
Cut the 4 toast slices into rounds using a large glass. Top each with chicken slices, tomato slices, and mozzarella slices.
Place the assembled toast on a baking sheet. Bake in a preheated oven at 200°C (392°F) for 10 minutes until the cheese melts and the chicken is cooked through (74°C / 165°F internal temperature). Garnish with basil.