Line a baking sheet with parchment paper or a silicone mat and set aside.
In a small saucepan over low heat, combine the peanut butter, honey and coconut oil. Stir constantly until the mixture is smooth and just warmed through — about 2–3 minutes. Remove from heat before it begins to boil.
Whisk the cocoa powder, vanilla and fine sea salt into the warm peanut mixture until fully incorporated and glossy.
Transfer the mixture to a mixing bowl, then fold in the quick-cooking oats and chopped peanuts with a spatula until evenly coated. Let the mixture sit 1–2 minutes so the oats absorb some of the liquid and the mix thickens slightly.
If the mixture seems too loose, return the bowl briefly to the still-warm (but turned-off) saucepan and stir over very low heat for 30–45 seconds to tighten the texture—do not overheat.
Using a tablespoon or small cookie scoop, drop rounded portions onto the prepared sheet about 1 inch apart. Gently press the tops with the back of the spoon to compact each cookie if you prefer a smoother surface.
Chill the pan in the refrigerator for 25–30 minutes, or place in the freezer for 10–12 minutes, until the cookies are firm to the touch.
Before serving, sprinkle each cookie with a tiny pinch of flaky sea salt if using. Store leftovers in an airtight container in the refrigerator for up to 1 week.