In a large bowl, combine beef, lime juice, orange juice, grated onion, cilantro, garlic, jalapeños, chili flakes, cumin, paprika, and salt. Mix by hand for about 1 minute.
Divide into 4 portions and form into firm, 1-inch thick patties.
Heat oil in a skillet over medium-high. Sear patties 5–6 minutes per side. Add cheddar during the last 1–2 minutes to melt.
Mash avocado with lime juice, orange juice, onion, jalapeños, and salt until half creamy, half chunky.
Combine tomatoes, red onion, cilantro, lime juice, and salt in a bowl. Stir gently.
Toast buns if desired. Add lettuce (optional), patty with cheese, guacamole, and pico de gallo. Top with bun and serve.