1. Preheat the oven to 425° F. Wash the vegetables.
2. Cut off the green tops of the leeks. Trim the root off the leeks. Starting at one end, cut the leek into thin round slices (1/2 inch to 1 inch). See notes for alternative cutting options. Place into a bowl of water to help remove sediment.
3. While the leeks are sitting, slice the potatoes into quarters. Then, peel and slice the red onion into thin strips.
4. Remove the leeks from the water, and place all vegetables into a clean mixing bowl.
5. Add 1 minced garlic clove, 1/3 cup olive oil (adjust as desired), 1 Tablespoon balsamic vinegar, 1/4 teaspoon of sea salt, 1/4 teaspoon or more of the black pepper, and a squeeze of lemon juice.
6. Toss all of the ingredients together until the vegetables are well-coated. Arrange the vegetables on a sheet pan in a single layer. 
7. Roast at 425° F in the oven for 30-35 minutes. TIP – Halfway through roasting, flip over the potatoes and check the leeks/onion for doneness. If the leeks/onion are fully cooked, remove them from the oven, and place them on a serving plate/bowl. (See notes for alternative cooking tips). Continue to cook the potatoes for the full amount of time.
8. Once the potatoes are done, remove from the oven, and combine them with leeks/onion. Season with extra salt/pepper, if desired.  
9. If adding greens, lightly steam the greens in microwave or stovetop until softened. 
10. Mix the steamed greens together with the potato, leeks, and onions.
11. Toss with fresh lemon juice and herbs to garnish. Serve immediately.
12. Storage: To store, let the potato and leek roast cool. Then, pace it in an airtight container. Best kept in the fridge for up to 4 days. To reheat from the fridge, place the leek and potato roast in an oven-safe dish. Warm in the oven at 350° F for 5-10 minutes or until the desired temperature is reached.

Air Fryer Option: 

1. Preheat the air fryer to 400° F. 
2. Spray the air fryer basket with cooking oil spray. Place seasoned diced potatoes in the air fryer and cook for 10 minutes. Shake basket and stir potatoes.
3. If adding leeks and onions, add them to the air fryer basket with the potatoes and proceed to cook an additional 8-10 minutes or until potatoes are golden and tender.