Preheat grill to medium-high (400°F to 450°F); or heat a grill pan over medium-high, and lightly grease. Place potatoes and water in a medium-size microwavable bowl; cover tightly with plastic wrap. Microwave on HIGH until tender, about 4 minutes. Spread potatoes on a plate lined with paper towels; let stand 10 minutes.

Combine salt, ancho chile powder, paprika, brown sugar, cumin, dry mustard, coriander, and oil in a large bowl. Add steak, onion, bell pepper, and potatoes; toss to coat. Thread mixture, alternating steak, onion, bell pepper, and potatoes, onto 8 (8-inch) skewers; place on lightly greased grill grate or in grill pan. Grill, uncovered, until potatoes, pepper, and onions are tender and steak is charred and cooked to desired degree of doneness (about 10 minutes per side for medium), turning occasionally.