Preheat the oven to 400°F (200°C) and line a large rimmed baking sheet with parchment paper.
In a small mixing bowl, whisk together the olive oil, minced garlic, lemon juice, dried oregano, salt, and pepper to create the marinade.
Place the chicken thighs and potato chunks on the prepared sheet pan.
Drizzle 3 tablespoons of the marinade over the chicken and potatoes, tossing the potatoes and rubbing the chicken to ensure even coating.
Arrange the lemon slices around the chicken and potatoes.
Roast in the center of the oven for 20 minutes.
Remove the sheet pan and add the asparagus spears to the remaining space. Drizzle the remaining marinade over the asparagus.
Return the pan to the oven and roast for an additional 12 to 15 minutes until the chicken reaches an internal temperature of 165°F (74°C) and potatoes are fork-tender.
Switch the oven to broil for 2 minutes if additional browning on chicken skin is desired.
Garnish with fresh parsley and serve immediately.