Place potatoes in a large pot and cover with cold water. Add a pinch of salt and bring to a boil.
Reduce heat and simmer potatoes until tender, about 15-20 minutes.
While potatoes cook, steam broccoli, carrots, and snap peas for 5-7 minutes until crisp-tender.
Drain potatoes and return to pot. Add butter and warm milk, then mash until smooth and creamy.
Season mashed potatoes with salt and pepper to taste.
In a bowl, toss steamed vegetables with olive oil, lemon juice, garlic powder, salt, and pepper.
Serve mashed potatoes alongside the seasoned steamed vegetables.