To prepare jam, grate tomatoes, flesh side down, over a large bowl to form 5 1/2 cups pulp; discard skins. Combine pulp, sugar, onion, 3 garlic cloves, and 2 jalapeños in a medium saucepan; bring to a boil. Reduce heat, and simmer until reduced to 2 1/4 cups (about 20 minutes), stirring occasionally. Cool to room temperature. Stir in cilantro, 3 tablespoons juice, and 1/4 teaspoon salt.
To prepare steak, combine rind, 1/3 cup juice, oil, 2 jalapeños, and 2 garlic cloves in a large zip-top plastic bag. Add steak; seal. Marinate in refrigerator 8 hours or overnight, turning bag occasionally.
Remove steak from bag; discard marinade. Sprinkle both sides of steak evenly with 1/2 teaspoon salt. Place steak on a grill rack coated with cooking spray; grill 3 minutes on each side or until desired degree of doneness. Let stand 5 minutes. Cut steak diagonally across the grain into thin slices. Serve with jam. Garnish with lemon slices, if desired.
Wine note: Tomato Jam captures the rich flavor of summer tomatoes, a classic partner for high-acid red wines. For a sure bet, reach for Chianti or an affordable barbera, like Michele Chiarlo Barbera d'Asti Le Orme 2004 ($13). This bright and fruity wine has tart cranberry flavors and the vibrant acidity that tomatoes demand. Earthy and smoky aromas resonate with the grilled steak. --Jeffery Lindenmuth