Grilled Red-Chile Steak with Sweet Plantains, Red Onion and Chipotle Salsa

ingredients

For the Garlicky Ancho Chile Rub
4 cloves garlic, peeled and finely chopped or crushed through a garlic press
1/3 cup ground ancho chile powder (available from national companies such as McCormick, Mexican groceries and internet sites)
4 teaspoons brown sugar
1 teaspoon dried oregano, preferably Mexican
1/2 teaspoon ground cumin
4 teaspoons ground black pepper
Salt
A 1 1/4-pound flank steak (or an equivalent weight of strip steak, rib-eye, chuck steak or whatever else may be your favorite)
2 black-ripe plantains
Vegetable oil
1 medium red onion, sliced into 1/4-inch-thick rounds
3 garlic cloves, peeled
4 medium (about 8 ounces total) tomatillos, husked, rinsed and cut in half
2 canned chipotle chiles en adobo (or more, if you like really spicy salsa)
Salt