Thaw the strawberries in a saucepan. Then add 1 tablespoon of water and heat everything on the stove. Peel the banana and mash it with a fork. Add the banana, chia seeds, lemon zest and vanilla to the strawberries and remove the pan from the heat.
Mix in finely chopped basil leaves (approx. 5 leaves) if desired. Basil goes perfectly with strawberries and gives the jam an additional fine note.
Finely puree the mixture with a hand blender and pour into a small mason jar. Let the jam rest for at least 30 minutes, better 24 hours, so that the chia seeds can swell.