Bring the lentils, water, bay leaf, and salt to a boil over medium-high heat. Reduce to medium-low, cover, and let cook until lentils are tender – about 15 minutes (may vary depending on variety of lentil). Drain and discard bay leaf.

Meanwhile, heat a tablespoon of olive in a large skillet. Add the chopped onion, carrot, celery, garlic, and thyme and a large pinch or two of salt. Cook until vegetables are softened, 8-10 minutes.

To make the vinaigrette, whisk together the red wine vinegar, 4 tablespoons olive oil, mustard, salt and pepper.

Combine the drained lentils, cooked vegetables, and vinaigrette. Taste and adjust salt as desired. Top with chopped parsley and crumbled feta. Serve warm or room temperature.