Fajita Taco Salad

For the dressing (makes about 6 tablespoons):

• 3 tablespoons mayonnaise
• 1 ½ tablespoons full-fat sour cream
• 1 ½ tablespoons whole milk
• ⅜ teaspoon lemon juice, more to taste
• 1 small garlic clove, peeled and minced or pressed through a garlic press
• ½ teaspoon chili powder*
• ¾ teaspoon dried oregano
• 1 ½ teaspoons mild olive oil
• Salt, to taste

For the beef and vegetables:

• 8 ounces sirloin steak**, cut into ¾-inch pieces
• 1 tablespoon mild olive oil
• ½ small red bell pepper, sliced into thin strips
• 1 large or 2 small jalapeno peppers, seeds and ribs (the white membranes) removed and sliced into thin strips
• ¼ red onion, peeled and sliced into thin wedges

For the salad:

• 4 cups shredded romaine lettuce
• 1 ounce grated cheese, such as monterey jack or cheddar
• 10 Doritos, crumbled