Place the spinach in a pan with a small amount of water, then cover and cook until wilted. Drain and squeeze dry.
Heat 2 nonstick frying pans, add 1 tortilla to each and crumble a quarter of the goats' cheese, followed by a quarter of the spinach and sun-dried tomatoes, over each tortilla. Season well.
Place 1 tortilla on top of each and cook over a medium heat for 3–4 minutes until golden underneath. Gently turn the quesadillas over and cook for a further 3–4 minutes. Remove from the pans and keep warm. Repeat with the remaining 4 tortillas.
Meanwhile, mix together the avocados, onion, lime juice and coriander in a bowl.
Serve the quesadillas in wedges with the avocado salsa.