Preheat oven to 425 F; coat a 3-qt. baking dish with nonstick spray. Preheat grill to medium-high.
Saute onion in oil in a saute pan for 5-6 minutes. Add garlic, cook 1 minute, then stir in beans. Add broth and reduce until liquid is evaporated. Stir in goat cheese.
Fill each tortilla with 1/3 cup bean mixture and roll to enclose. Place in the prepared dish, seam side down. Top with Jack cheese and bake until cheese melts, 20 minutes.
Combine juices, tequila, brown sugar, and salt for the marinade in a resealable plastic bag. Add steak; marinate 15 minutes. Grill, covered, 4-5 minutes per side for medium-rare. Transfer to a cutting board, tent with foil, and rest 5 minutes before slicing. To serve, spoon Tomatillo Guacamole on plates, top with enchiladas and steak slices. Garnish with sour cream.