Preheat oven to 400 degrees and line a baking sheet with parchment paper.
In a large bowl, add the baby potatoes and red beets. Add the olive oil, garlic, salt, pepper, and thyme. Stir to combine. Transfer the potatoes and beets to the baking sheet in a single layer. Bake for 45-50 minutes, or until veggies are tender, turning every 15 minutes or so.
While the vegetables are cooking, make the Sweet Mustard Salad Dressing.
When potatoes and beets are ready, assemble the salads. For each serving, in a bowl, add lettuce topped with parsley, potatoes, beets and walnuts. Serve with the Sweet Mustard Salad Dressing. Best served immediately.