Combine the steak rub ingredients–garlic powder, sage, salt and 1/2 teaspoon of dried thyme–in a small ball and set aside.
Start making the mushroom sauce. Heat the olive oil over medium heat in a skillet. Add the onions, and cook until they have browned, about 10 minutes.
Add the garlic to the skillet, cook for another minute.
Stir in the mushrooms, cook until they begin to “sweat” (moisture starts coming out), about 5 minutes.
Stir the red wine into the skillet with the mushrooms, and add the 1 teaspoon thyme and salt and pepper to taste. Simmer until the wine is mostly absorbed, which takes 3 to 5 minutes.
Finish the mushroom sauce by stirring in the butter, and letting it gradually melt. Cover the sauce pan and keep warm while you cook the steaks.
Around the time you add the wine to the mushrooms, preheat a grill to medium high. Lay the steaks out on a work surface. Sprinkle roughly half of the spice mixture onto the steaks, and rub into the meat. Turn the steaks over, and repeat the rubbing process. Let the steaks sit with the rub as the mushroom sauce gets finished up.
Spray the grill with some oil spray, then add the steaks to the grill. Grill covered on direct heat for about 6 minutes, then turn the steaks over. Grill for another 6 minutes or so for medium rare. Check steaks for doneness, as cooking times will vary based on your grill and thickness of steaks.
Remove steaks to a platter, and let them rest briefly.
To serve, slice the steaks crosswise, and place 4 or 5 strips on a plate. Scoop some mushroom sauce over the steaks, and repeat the plating process for additional servings. Enjoy!