Chicken Tostadas

INGREDIENTS

• 1 or 2 fresh serrano chiles, stemmed
• 1 avocado, halved, pitted, and peeled
• 6 large radishes, halved and sliced
• 1/2 cup Mexican or sour cream
• 1 rotisserie chicken, meat coarsely shredded (4 cups)
• 1/4 cup crumbled queso añjo (aged white cheese, also called ) or ricotta salata
• 1 medium white onion
• 1/2 cup chopped cilantro, divided
• 3 cups shredded iceberg lettuce
• 6 (6-inch) corn tortillas
• 1 (1-pound) can refried beans, heated
• 2 large garlic cloves
• 1/2 cup plus 2 tablespoon vegetable oil, divided
• 1 pound tomatoes, quartered