Buzz the rolled oats in a food processor, adding in the chopped nuts, a little at a time, until the mixture is coarse.
Blend together the butter and ½ cup of sugar and beat with a hand mixer until it is very fluffy. Beat in the vanilla, salt and cinnamon. Add the flour and the oat-nut mixture and mix together well, using your hands. Shape into a flat disk, then press the disk into the bottom and sides of a 10 ½ inch fluted tart pan, making a layer all around about 1⁄8 inch thick. Trim the top level with the top of the tart pan and use the extra bits to patch any holes in the dough. Wrap in plastic wrap and set in the refrigerator or freezer for at least 30 minutes, until very cold. (If you must leave it for more than an hour or so, make sure the plastic wrap is sealed around it to prevent the dough from drying out.)
When ready to cook, set the oven on 400° F. Once the oven is hot, set the pan in it and bake 12 to 15 minutes or until the crust is lightly golden, weighing it down with pie beans if necessary.
While the crust is browning, combine in a bowl the blueberries, lemon zest, cornstarch and 2 tablespoons of the remaining sugar. Toss the berries vigorously with a fork, just enough to bruise some of them lightly.
When the crust is done, remove the pan from the oven and, using a dish towel to protect your knuckles, gently press the dough crust, which will have risen a bit, back into shape. Turn the contents of the bowl of berries into the pie crust. If the top edge of the crust is already brown, set a protective ring on it (or cover the edge with aluminum foil) to keep it from getting too dark. Transfer the tart pan to the oven and bake for about 25 minutes.
Remove the tart from the oven and set aside. Melt the optional jelly or jam in a saucepan and when the tart is cooled to room temperature spoon it over the berries to make a light glaze. Refrigerate for at least 15 minutes before serving. Serve the tart as is, or top with a spoonful of whipped cream or vanilla ice cream.