Heat the oven to 200 C / 400 F. Set a wire rack inside a 13 x 18 inch / 33 x 46 cm sheet pan and lightly oil the rack.

Pound the chicken breasts between two sheets of plastic wrap to an even 1.5 cm thickness. Season both sides with salt and pepper.

Set up three shallow dishes: one with flour, one with eggs whisked together with dijon mustard, and one with walnuts, panko, parmesan and garlic powder stirred together.

Dredge each chicken breast in the flour, shaking off excess, then dip in the egg mixture, then press firmly into the walnut crumb until fully coated on both sides.

Place the chicken on the rack and drizzle the tops with olive oil. Bake for 20 to 25 minutes, until the crust is deep golden and a thermometer reads 165 F / 74 C at the thickest point.

About 5 minutes before the chicken is done, heat 1 tbsp olive oil in a 10-inch / 25 cm skillet over medium heat. Add the garlic and cook 30 seconds until fragrant.

Add the spinach in batches, tossing until just wilted, about 2 to 3 minutes. Squeeze the lemon juice over the top and season with salt and red pepper flakes if using.

Rest the chicken for 3 minutes, then slice or plate whole over the greens.