Step 1

Blend cilantro, mint, lime juice, chile, garlic, cumin seeds, sugar, salt, and ¼ cup water in a blender until smooth, about 1 minute. Transfer purée to a small bowl. Gradually add oil, whisking constantly until emulsified. Set chutney aside.

Step 2

Bring lentils, salt, and 2½ cups water to a boil in a medium pot. Reduce heat to medium, cover, and cook until lentils are tender and liquid is absorbed, about 30 minutes. Remove from heat.Do ahead: Lentils can be cooked 5 days ahead. Let cool, then transfer to an airtight container. Cover and chill.

Step 3

Remove toughest outer leaves from cauliflower (leave the tender inner leaves) and trim 1" off bottom of stem. Resting cauliflower on crown and starting at stem end, cut lengthwise into thirds. Trim off outer edges of crown from both outside pieces to create three 1"-thick steaks; reserve trimmed-off florets for another use. Repeat with broccoli. Arrange broccoli and cauliflower steaks on a large baking sheet; drizzle with oil and season both sides with salt.

Step 4

Prepare a grill for medium indirect heat (for a charcoal grill, bank coals on one side of grill; for a gas grill, leave one or two burners off). Place broccoli and cauliflower on grate over indirect heat. Cover and grill until tender, 15–20 minutes. Uncover and move steaks over to direct heat; continue to grill until they are golden brown and edges are charred, about 2 minutes per side.

Step 5

Arrange lentils on a platter and drizzle half of the chutney over. Place cauliflower and broccoli steaks on top. Drizzle with remaining chutney and top with pumpkin seeds and herbs.