Make the jalapeño chimichurri lentils. Place the lentils in a medium saucepan and cover them with water by about 2 inches. Put the saucepan on the stove over medium-high heat. Bring lentils to a boil and then lower them to a simmer. Cook until lentils are just-tender, about 25 minutes. Drain.
While lentils are cooking, make the jalapeño chimichurri. Finely chop the parsley and transfer to a medium bowl. To the parsley, add the jalapeño, garlic, capers, olive oil, lemon juice, salt, and red pepper flakes. Stir to combine and check for seasoning. Adjust if necessary.
Stir the warm lentils into the jalapeño chimichurri. Once thoroughly mixed, just set the lentils aside at room temperature.
Make the maple mustard tahini. In a medium bowl, whisk together the tahini, lemon juice, maple syrup, mustard, and salt until combined. Then, vigorously whisk in the cold water. The sauce should thin out a bit and become more pale and creamy in colour. Set aside.
Grill the cabbage. Preheat your grill to medium high heat. Cut the cabbage into 1 ½ inch-thick “steaks.” Set the cabbage on the cutting board so that the core is facing up. Then cut 4 round steaks through the middle section so that each piece has a bit of the core intact (this is what will hold it together on the grill). Save the rest of the cabbage for another use.
Place cabbage steaks on a baking sheet. Spray one side with avocado oil spray and season with half of the steak spice, salt, and pepper. Repeat with the other side and remaining steak spice.
Place the cabbage steaks on the grill and close the lid. Cook for 5 whole minutes, or until charred on one side. Using both tongs and a flipper, carefully flip the steaks over. Close the lid and cook cabbage steaks for another 5 minutes, or until charred on the other side and soft in the center.
Remove the cabbage steaks from the grill and serve with the jalaleño chimichurri lentils, maple mustard tahini sauce, extra chopped parsley, and chili flakes (if desired).