Combine sun dried tomatoes, garlic, basil, avocado, olive oil and salt & pepper in a food processor and pulse until combined.
For the Panini
Heat a grill pan or outdoor grill to medium high.
Spray with cooking spray and layer zucchini slices on.
Grill for 3-4 minutes per side depending how thick the slices. You want them cooked through with grill marks but still retaining a slight bite to them.
Remove zucchini and set aside.
Spread goat cheese on one piece of bread for each sandwich.
Spread pesto on the other piece of bread for each sandwich.
Layer zucchini and tomatoes on top of one slice of bread and cover with the remaining slice.
Place sandwiches on a heated panini press and cook/press for about 5 minutes until goat cheese starts to melt.
While panini cooks, heat a small sauce pan with balsamic vinegar to medium. Simmer and cook until reduced and vinegar becomes thick and syrup-like. It should just start sticking to a spoon when ready.
Remove panini from press and drizzle balsamic reduction on top or use as a dip in a small side bowl.