Combine 2 teaspoons of the brown sugar, the chili powder, cumin, pepper, and salt in a small bowl.

Spray a small saucepan with nonstick spray and heat over medium-low. Add the onion and cook, stirring frequently, until softened, about 4 minutes.

Add 1 tablespoon of the spice mixture, the remaining 1 tsp of brown sugar, the ketchup, water, steak sauce, and Worcestershire sauce; bring to a boil.

Reduce the heat and cook, covered, stirring occasionally, until the flavors are blended, 10 minutes.

Set aside and keep warm.

Spray the grill rack with nonstick spray and heat the grill to medium-high or prepare a medium-hot fire.

Rub the steaks with the remaining spice mixture.

Place on the grill rack and grill until an instant-read thermometer inserted into the side of each steak registers 130 degrees, 3-4 minutes on each side.

Transfer to a platter, cover loosely with foil and let stand 5 minutes (until the temperature increases to 135 degrees for medium-rare).

Serve with the sauce.