In a large saucepan, combine brown rice and either stock or water. Cook rice according to package directions.
While rice is cooking, prepare lentils as follows: In a medium saucepan, combine the lentils, bay leaf and 4 cups of water. Cover and bring to a boil. Reduce heat and gently boil uncovered for 15 minutes or until the lentils are tender but still have a bite.
While rice and lentils are cooking, thinly slice the scallions, and cut the red peppers and zucchini into small ½ inch dice (remove any large seeds from the zucchini if necessary).
Drain the lentils and discard the bay leaf. Transfer to a large bowl. Add the cooked rice, scallions, red pepper, zucchini, feta, oil, vinegar, thyme, salt and pepper and combine with a large spoon.
Serve warm or at room temperature with additional feta cheese crumbled over the top.