Heat a tablespoon of olive oil in a skillet over medium heat.
Add thinly sliced red onion to the pan.
Cook over medium-low heat for 12–15 minutes until onions turn golden and sweet.
Season onions toward the end of cooking with fresh ground pepper for fresher flavor.
Remove onions from skillet and set aside.
Lightly coat the skillet or brush tortillas with a thin layer of oil before toasting.
Sprinkle grated Colby-Jack cheese evenly over tortilla.
Add a layer of caramelized onions on top.
Scatter crumbled goat cheese over the filling.
Cover with another tortilla and press gently.
Cook until bottom is golden, then flip and toast other side.
Slice quesadilla and serve warm with sour cream and salsa.