Grilled Flank Steak with Charred Tomato Relish

INGREDIENTS

medium-size plum, Roma or Campari tomatoes, halved lengthwise

small sweet onion, in quarters

3 tbsp

olive oil, divided

2 tsp

kosher salt, divided

1 1/4 tsp

black pepper, divided

1 1/2 lb

Flank steak

1 tbsp

balsamic or red wine vinegar

garlic clove, finely chopped

1/2 tsp

granulated sugar