In 3-quart saucepan, bring 1 quart water to boil. Add potatoes and 2 teaspoons salt; cook covered, 10 to 12 minutes until just tender. Drain. In large nonstick skillet over medium heat, break up sausage and saute with onions about 10 minutes, stirring occasionally, until sausage is cooked through and onions are tender. Drain and discard excess fat. Add potatoes to skillet; cook and toss until potatoes begin to brown. Keep warm. To make Avocado Salsa, add tomatillos, chiles and garlic to container of electric blender or food processor; pulse on and off, scraping sides of container as needed, until finely chopped. Add avocado; blend until almost smooth. Season with salt to taste. Fill tortillas with potato mixture; accompany with salsa.