How to Make It
Sprinkle salt, chili powder, and cumin on 1 side of the steak. Heat oil in a large skillet over high. Sear steak, seasoned side down, for 2 minutes. Flip, and cook 30 seconds longer. Remove from heat.
Arrange onion slices on bottom of slow cooker, and top with seared steak. Spread bell pepper strips over steak, and top with salsa. Cover and cook on high for 2 hours or on low for 4 hours.
Transfer steak to a cutting board; let stand 5 minutes. Thinly slice against the grain. Return sliced steak to slow cooker. Add fresh lime juice, and let stand 5 minutes before serving. The meat and veggies may also be held on warm in the slow cooker until ready to serve, up to 1 hour. Prepare tortillas according to package directions. Serve steak and veggies inside tortillas with desired toppings.