Coat a medium skillet with cooking spray; place over medium-high heat until hot. Add onion and garlic; cook 5 minutes, stirring constantly. Add cooked rice, 1/2 teaspoon chili powder, 1/2 teaspoon cumin, 1/8 teaspoon red pepper, 1/8 teaspoon coriander, and beans; cook until thoroughly heated, stirring occasionally. Remove from heat, and cool. Cover and chill.
Combine ranch dressing, remaining chili powder, cumin, red pepper, and coriander; set aside.
Combine lettuce and next 5 ingredients in a large bowl, tossing well. Add reserved rice mixture and salad dressing; toss gently to coat. Cover and chill. Just before serving, place tortilla chips on a serving platter; spoon salad over chips.