Place lentils in a medium saucepan; cover with cold water by 2 inches. Bring to a boil. Reduce heat, and simmer, partially covered, stirring occasionally, until lentils are tender, about 20 minutes. Drain and transfer lentils to a medium mixing bowl.
Preheat oven to 450 degrees. Toss zucchini, yellow squash and onion with olive oil; season with salt and pepper. Place on a rimmed baking sheet and roast until vegetables are tender and browned, about 10-15 minutes. Remove from oven and allow to cool at room temperature.
Combine vinegar and mustard. Pour in oil in a slow, steady stream, whisking constantly until emulsified. Add chopped onion. Season with salt and pepper. Toss lentils with half the vinaigrette; let cool.
In a large bowl, combine Fresh Express Spinach & Arugula salad and tomatoes. Add the lentils and toss to combine. Divide salad onto 4 plates. Top with roasted vegetables and goat cheese. Drizzle remaining vinaigrette over the salads and serve.