Preheat the oven to 400 degrees F. Place the potatoes on a baking sheet and drizzle 1 tablespoon olive oil all over the potatoes. Sprinkle the garlic powder and some salt and pepper on top. Toss with your hands to coat all sides of the potatoes with the oil and seasoning. Bake, rotating the pan and flipping the potatoes halfway through, until fork-tender, 20 to 25 minutes.
Meanwhile, add the remaining teaspoon olive oil to a large skillet over medium-high heat. Sprinkle the Italian seasoning, 1/2 teaspoon salt and 1/4 teaspoon pepper onto the chicken breasts and gently pat it down with your fingers. Add the chicken breasts to the hot skillet and brown on both sides, 3 to 4 minutes per side. Remove from the skillet and reduce the heat to low.
Melt the butter in the skillet then sprinkle flour on top of the butter. Whisk to cook off the raw flour taste, 1 minute, then carefully add the chicken stock, vigorously whisking. Add the lemon zest and juice. Let cook, whisking occasionally, until thickened, 5 to 7 minutes. Add the asparagus to the pot and cook until the asparagus has softened but is still bright green, about 7 minutes.
Add the chicken back into the skillet and cook to ensure it's cooked thoroughly, another 3 minutes. Coat the chicken with sauce from the pan.
Place 1 piece of chicken on each of 2 plates, then divide the roasted potatoes between the plates next to the chicken. Place half of the asparagus on each plate and drizzle some sauce on top. Use the juice of the remaining lemon half on top of the dish if you desire more lemon flavor.