Preheat the oven to 425 degrees F. You can microwave the squash for 3-5 minutes to soften the skin in order to cut through it. Once softened, cut the squash down the center lengthwise, seed it and cut into half moons about 1/2 inch thick. Place the squash slices, red onion quarters and sage leaves on a rimmed sheet tray and coat with olive oil, salt and pepper. Roast the vegetables for 20-25 minutes until cooked through and slightly charred.
While the vegetables are roasting, cook the lentils according to the package instructions. You can use water or broth for the liquid and a pinch of salt. Drain and set aside the lentils to cool, once cooked.
In a large bowl, combine the cooked lentils with the lemon zest and juice, mint and tarragon. Add the roasted squash and onions. Taste and adjust the seasoning. Garnish with a drizzle of olive oil and serve.