Whisk together the dry ingredients, then whisk in 3/4 cup hot water. Stir in the rest of the ingredients.
Coat a skillet with cooking spray and heat over medium heat. Add the batter to the skillet 1/4 cup at a time to form patties. Reduce the heat to medium-low and cook until they're golden on that side, then flip and cook until they're golden on the other side. You should have enough batter for 8 patties.
Mix the topping ingredients together and serve atop the croquettes. I usually make my topping mixture ahead and chill it because I like the contrast of the chilled topping and the warm croquettes.