Mix the oats, nuts, seeds, melted oil, honey, vanilla and cinnamon together in a bowl until thoroughly coated.
Press about 3 tablespoons of the mixture into 8 greased mini tart pans. Use the back of an oiled spoon to help press the granola evenly across the pan and up the sides.
Bake in the center rack of the oven for about 15 to 17 minutes, or until golden.
Immediately after removing the tart shells from the oven, use the back of the spoon to press down the centers of the crust to create more of an indentation, and push up the sides. The shell puffs up in the oven, so it helps to reshape the crust after it bakes while still hot.
Allow to cool completely in the pan before removing.
Use a small knife to gently release the sides of the crust, working around each side, then very carefully remove it from the pan, turning over if needed into your hand. The crust should be crisp on the sides and hold together, but will be delicate.
Fill each tart with 3 to 4 tablespoons yogurt, smooth out evenly.
Arrange the fruit on top and serve immediately. The crust will become a little soggy if left to sit for too long.
The baked granola crusts can be stored for up to a day before in an airtight container in a single layer, do not stack them!
You can make this tart in a large 10-inch tart pan with removable bottom. You may need up to 3 cups yogurt for the larger size. Use a thick Greek-style yogurt, or strained yogurt to make serving easier.
You can use any flavor yogurt you like. Add honey, maple syrup or vanilla to sweeten up plain yogurt if desired.
Butter can be substituted for coconut oil.
Pistachios, peanuts or almonds can be substituted for walnuts.
Maple syrup or agave syrup can be substituted for honey.