Slice the chicken breasts into 1-inch thick cutlets, then pound each piece to an even 1/2-inch thickness using a meat mallet—this ensures even cooking and creates the perfect burger patty size. In a shallow bowl, whisk together the buttermilk and egg to create the marinade base. Submerge the flattened chicken cutlets in this mixture and refrigerate for at least 1 hour. While the chicken marinates, slice your tomato into 1/4-inch rounds, thinly slice the red onion, and prepare the avocado. I prefer to slice everything just before assembly to keep the vegetables as fresh as possible.
In one shallow dish, combine the flour, whole wheat flour, panko bread crumbs, paprika, smoked paprika, chili flakes, garlic powder, onion powder, salt, pepper, baking powder, and oregano—this creates your seasoned coating blend. In a small bowl, whisk together the honey mustard sauce ingredients: marmalade, honey, mayo, mustard, garlic powder, salt, and pepper. The marmalade adds a subtle citrus sweetness that balances the mustard's tang beautifully.
Mix the remaining mayo with 1/2 tsp garlic powder and a pinch of salt and black pepper to create a simple garlic spread. Butter the insides of your buns and toast them in a skillet or oven at 350°F for 2-3 minutes until golden—toasting prevents the buns from getting soggy and adds a subtle nutty flavor that complements the chicken.
Heat the grapeseed oil to 350-375°F in a large, heavy-bottomed skillet or Dutch oven. While the oil reaches temperature, remove the marinated chicken from the refrigerator and working with one cutlet at a time, dredge it thoroughly in the dry coating mixture from Step 2, pressing gently so the coating adheres. Make sure each piece is completely covered for maximum crispiness.
Carefully place the coated chicken cutlets into the hot oil, working in batches if necessary to avoid overcrowding the pan. Fry for 5-8 minutes, turning halfway through, until the coating is deep golden brown and the internal temperature reaches 165°F. Transfer the fried chicken to a paper towel-lined plate to drain excess oil. I like to season each piece with a light sprinkle of salt immediately after frying while the coating is still slightly warm—it helps the salt adhere better.
Spread the garlic mayo from Step 3 on the bottom bun, then layer with lettuce, a tomato slice, red onion, and avocado. Top with a fried chicken cutlet from Step 5, then generously spread the honey mustard sauce from Step 2 on the inside of the top bun. Add pickled jalapeños for a spicy kick if desired, then close the burger and serve immediately while the chicken is still warm and crispy.