Preheat your oven to 400°F and line a large sheet pan with parchment paper for easy cleanup.
Scrub the red potatoes and dice them into 1-inch cubes to ensure they roast at the same rate as the chicken.
Trim the tough woody ends off the broccolini stalks and set the florets aside.
In a small bowl, whisk together the extra virgin olive oil, lemon juice, minced garlic, dried oregano, sea salt, and black pepper to create a bright marinade.
Place the chicken thighs and diced potatoes in a large mixing bowl, pour over most of the marinade, and toss until every piece is well-coated.
Spread the chicken and potatoes in a single layer on the prepared sheet pan, ensuring they aren't overcrowded so they crisp up properly.
Roast in the center of the oven for 15 minutes.
Remove the pan from the oven, add the broccolini to the empty spaces, and drizzle with the remaining marinade.
Return the pan to the oven for another 10-12 minutes until the chicken is cooked through and the potatoes are tender and golden.