Preheat the oven to 425.
Drizzle olive oil on the bottom of a large sheet pan, season with salt and place the sweet potatoes face down. Drizzle the tops with the oil and season with salt. Place in the oven for about 35 minutes, removing them from the oven at about 25 minutes. Flip them, move them to one side, then add the pecans to one side of the baking sheet and bake for 5 minutes. Remove the pecans from the sheet pan and allow the sweet potatoes to cook until tender.
While the sweet potatoes roast, make the crumble. Add the pecans and begin to chop them, then add the dates and do the same. Continue to add the feta and arugula, chopping after each ingredient is added. Add the salt, pepper and lemon zest and chop until the mixture is combined and a "crumble" is created.
Place the sweet potatoes on a plate, gently press down on each with a fork. Top with the crumble and the tahini mix (optional).
