What ingredient is primarily used for adding heat in Panda Express's spicy dishes?

Chili oil is primarily used for adding heat in Panda Express's spicy dishes because it is infused with chili peppers, which release their heat and flavor into the oil. This ingredient not only contributes a distinct spiciness but also enhances the overall flavor profile of the dishes it complements.

While black pepper, Sichuan peppercorns, and red pepper flakes do provide some level of heat, they each have different flavor characteristics and are not the primary source of heat used in the spicy selections at Panda Express. Black pepper has a more pungent bite, Sichuan peppercorns offer a numbing sensation along with a citrusy flavor, and red pepper flakes introduce a different texture and flavor. In contrast, chili oil integrates seamlessly into sauces and stir-fried dishes, making it the go-to ingredient for achieving the desired level of spiciness and flavor in a cohesive manner at Panda Express.