Wash the potatoes. Place in a pot and cover with water. Bring to a boil. Reduce the heat, but maintain a steady boil for about 20 minutes. You will know they are done when you can pierce the potato with a fork easily.
Remove pan from the burner, drain and let cool.
When they are cool, you can either leave the skin on or peel the skin off. Dice the potatoes; set aside.
You'll need to also cook your green beans and carrots. For the green beans if you don't have fresh, you can use frozen ones. Bring a small pot of water to a boil. Toss in the green beans and carrots. Cook for about 5 minutes. Drain and rinse under cold water; set aside.
To make your dressing combine oil, vinegar, garlic, mustard, thyme, salt, and pepper. Whisk together quickly until completely blended together; set aside.
Assemble the salad in a large bowl. Add the potatoes, green beans, carrots, green onions and spinach. Add to it the dressing and toss gently. Serve immediately.