Heat oven to 400°F. In 12-inch nonstick skillet, heat 2 tablespoons of the oil over medium-high heat. Add onion and potatoes; cook about 10 minutes, stirring occasionally, until potatoes are thoroughly cooked and slightly browned.
Meanwhile, cook spinach in microwave as directed on box. Drain spinach; cool 5 minutes. Carefully squeeze with paper towels to drain. Pull spinach apart into smaller pieces. Measure 4 teaspoons of the chiles; reserve remaining chiles for sauce.
Stir spinach, 4 teaspoons chiles, the salt, coriander, 1 teaspoon garam masala and 1/2 teaspoon ginger into potato mixture. Cook over medium heat 2 to 3 minutes, stirring frequently, until mixed and thoroughly heated. Remove from heat; gently stir in lemon juice.
Place about 1/4 cup potato filling on each tortilla, 1/2 inch from one side. Starting at side with filling, tightly roll up each tortilla around filling; place seam side down on ungreased cookie sheet. Brush taquitos with remaining 1 tablespoon oil.
Bake 8 to 11 minutes or until crispy and golden brown.
Meanwhile, in medium bowl, stir sauce ingredients until well mixed. Serve warm taquitos with sauce for dipping.