Lentil Kielbassoulet

Name: Lentil Kielbassoulet
Ingredients: ½ cup plus 3 Tbsp. extra-virgin olive oil, divided; 1 lb. wild mushrooms (such as maitake or oyster), torn into 2 pieces; 2½ tsp. kosher salt, divided; 1 lb. kielbasa sausage, cut 1 thick on a diagonal; 1 large fennel bulb, fronds finely chopped, bulb finely chopped; 1 large onion, finely chopped; 2 medium carrots, peeled, finely chopped; 2 celery stalks, finely chopped; 11 garlic cloves, 8 thinly sliced, 3 left whole; 1 Tbsp. thyme leaves; 1¼ tsp. hot smoked Spanish paprika; ½ tsp. crushed red pepper flakes; 3 Tbsp. double-concentrated tomato paste; 2 cups black beluga or French green lentils; 1 baguette, torn into 2 pieces