Coarsely chop cauliflower florets.
Stem and mince parsley.
Pat chicken breasts dry, and season both sides with a pinch of salt and pepper.
Cook the Cauliflower
Bring a medium pot with cauliflower, 1½ cups water, and ¼ tsp. salt to a boil.
Reduce heat to medium-high, and stir occasionally until water evaporates completely, 14-16 minutes.
Remove from burner and add sour cream and cheese.
Mash until mostly smooth, seasoning with a pinch of salt, if desired. Set aside.
While cauliflower cooks, toast crumbs.
Toast the Crumbs
Heat a medium oven-safe pan over medium-high heat. Add 1 tsp. olive oil and panko to hot pan.
Stir constantly until toasted, 1-2 minutes.
Transfer to a bowl and toss with half the parsley (reserve remaining for garnish).
Wipe pan clean and reserve.
Cook the Chicken
Return pan used for crumbs to medium-high heat.
Add 2 tsp. olive oil and chicken breasts to hot pan.
Cook undisturbed until browned on one side, 2-3 minutes.
Flip chicken and top with marinara. Place pan in oven and roast until chicken reaches a minimum internal temperature of 165 degrees, 10-12 minutes.
Remove from oven
Bake the Chicken
Place a dry towel on pan handle to indicate its hot.
Carefully, top chicken breasts with toasted crumbs.
Return to oven and toast, 1-2 minutes.
Plate as pictured on front of card, garnishing with remaining parsley.