Preheat oven to 425 degrees.
Toss the cauliflower with salt, pepper, half the mint, and 1 tsp of extra virgin olive oil. Place in a single layer on a baking sheet. Roast for 30 minutes, checking once halfway and turning the florets over to ensure they roast evenly.
While the cauliflower is roasting, make the lentils and couscous. For the lentils, place the lentils in a saucepan with water to cover by an inch, season with salt and pepper, bring to a boil, cover and cook 20 minutes or until the lentils are tender.
For the couscous, place a wide saucepan or skillet on the stove. Heat the remaining oil in the pan and add the onions and garlic. Saute over medium heat until the onions are translucent but not brown.
Add 2 cups of water (vegetable stock is even better), season with salt and black pepper, add the remaining mint, and bring the water to a boil. Add the couscous, stir it once, and turn off the heat. Place a lid on the saucepan and let the couscous stand at least 10 minutes.
To assemble your dish, add the lentils to the couscous, mix well, and check for seasoning. Stir in the mint, parsley or coriander, if using. At this point, a light drizzle of olive oil adds an even greater wallop of flavor to this dish, but it's optional.
Serve the lentils and couscous in a platter with the roasted cauliflower florets arranged on top.