Sunflower seed meal alternative

From the two i would use almond meal- from the recipe notes it sounds like the author just wanted to keep the recipe nut free.
Probably best to buy almond meal, trying to make it in a food processor can be tricky as it can turn into a paste

As long as you realize you will slightly change the flavor profile depending on what nut or seed meal you opt for- in my experience you can fairly easily sub one for another. I don't think I'd go for using sesame seed meal, since you'll be using tahini to make the caramel. Though chocolate usually covers a multitude of flavors, sesame is a rather strong one as well. You could find it takes over the brownies. Almond meal is the most blandish of the nut meals, and wouldn't likely compete. You could also consider walnut, pecan, or hazelnuts- understanding each will bring it's own particular flavor change. You can make any of these nuts or seed into meals using a food processor, or purchase them ready made. At any rate, all you can do is pick and try one, and see what you like. Seems to me that any culinary experiment involving chocolate and brownies can't go too far wrong.