Masala Burgers with Tangy Tamarind Sauce and Red Onion-Mint Relish

INGREDIENTS

• 2 teaspoons ground cayenne
• 1/4 cup extra-virgin olive oil, for brushing on the grill rack and buns (recommended: Colavita)
• 6 whole-wheat hamburger buns, split
• 2 pounds ground sirloin
• 1/4 cup extra-virgin olive oil (recommended: Colavita)
• 1/2 teaspoon kosher salt
• 1/2 head iceberg lettuce, sliced
• 1 teaspoon ground cumin
• 2 cups thinly sliced red onion
• 1 (14-ounce) package frozen tamarind pulp, thawed (recommended: Goya or La Fe brand)
• 3/4 cup light brown sugar
• 2 ounces fresh ginger, chopped
• 2 teaspoons kosher salt
• 2 medium-sized Roma tomatoes, thinly sliced lengthwise
• 2 ounces garlic cloves, chopped
• 2 tablespoons garam masala
• 2 tablespoons fresh lemon juice
• 1/2 cup chopped fresh mint leaves
• 1/2 teaspoon ground cayenne