For a milder dish, remove all seeds and membranes from the jalapeños, and for extra heat leave some seeds or add a pinch of cayenne to the filling. Make sure the cream cheese is fully softened so the filling mixes smoothly and is easy to spread. These stuffed chicken breasts can be assembled up to a day in advance and refrigerated before cooking; allow them to sit at room temperature for about 15 minutes while the oven preheats before baking. Leftovers keep well in the refrigerator for up to 3 days and reheat best in a 300°F oven or air fryer until warmed through.