
Place the lentils in a medium saucepan, cover them with water by about 2 inches, and boil. Lower to a simmer for about 25 minutes until just tender. Drain.
Chop parsley and combine with jalapeño, garlic, capers, olive oil, lemon juice, salt, and red pepper flakes. Stir and adjust seasoning.
Stir the warm lentils into the chimichurri and set aside at room temperature.
Whisk tahini, lemon juice, maple syrup, mustard, and salt together, then gradually whisk in cold water to thin.
Preheat grill to medium-high. Cut cabbage into 1 ½ inch-thick steaks, spray with oil and season. Grill for about 10 minutes total, flipping halfway, until charred and tender.
Remove cabbage steaks and serve with lentils, tahini, extra parsley, and chili flakes if desired.