Combine 1 tablespoon canola oil, lime juice, brown sugar, chile powder, and 1 minced garlic clove in a large zip-top plastic bag. Add steak; seal and toss to coat. Marinate at room temperature 30 minutes.
Heat a large grill pan over medium-high heat. Brush the remaining 1 tablespoon canola oil over onion slices, tomatoes, and bell pepper. Arrange the vegetables in pan; cook for 4 minutes on each side or until charred and softened.
Combine tomato, 1/4 teaspoon salt, and remaining garlic clove in a food processor or mini chopper; pulse until almost pureed. Place tomato mixture in a medium bowl. Coarsely chop onion and bell pepper; add to bowl. Stir in oregano and black pepper.
Heat a large cast-iron skillet over high heat. Coat pan with cooking spray. Add steak mixture to pan; cook for 6 minutes or until done, stirring frequently. Stir in remaining 3/8 teaspoon salt.
Heat tortillas according to the package directions. Arrange about 1 1/2 ounces steak on each tortilla; top each tortilla with about 2 tablespoons salsa and 1 1/2 teaspoons sour cream.