Add warm water NOT HOT, yeast, and sugar to a very large bowl. Let the mixture sit until foamy and bubbly, about 5-6 minutes. (If it does not foam and bubble, start over.)
While the yeast activates, add the spinach to a medium saute pan. Turn the heat on medium and toss spinach until wilted. Set aside.
Once the yeast has activated, pour in the flour, salt, chopped artichoke hearts, spinach, and four ounces of the feta. Reserve the remaining one ounce for later.
Use a wooden spoon to stir the mixture until everything is combined. Remove the dough on to a piece of parchment paper. Rinse the bowl out and wipe dry. Add 1/4 of olive oil to the bottom of the bowl. Use your hands to coat the sides of the bowl. Place the dough back in the bowl and then turn over to coat all of the dough. Place a kitchen dishtowel on top and store in a warm draft-free place until doubled in size, about 3 1/2-4 hours.
Once the dough has doubled in size, take two forks on either side of the dough and pull it up into the center. Turn the bowl 1/4 and repeat, do this two more times until you have a ball of dough.
Add another tablespoon of olive oil to a 9x13 metal baking pan. Use your hands to coat the whole pan with oil. Add another tablespoon of olive oil and transfer the dough to the pan. Gently toss the dough in the oil and then and press down slightly. (You do not need to push it all the way to the edges, it is going to rise one more time and then you can stretch the dough as needed.)
Cover with the same kitchen towel and let it rise again until doubled in size, about 1-2 hours. Preheat oven to 425 degrees.
Once the dough has risen again, rub your hands with olive oil. If the dough has not covered the entire pan, use your hands to gently pull it into all the corners. Next, use your fingers to press dimples into the dough, don't be gentle! Brush with remaining tablespoon of olive oil.
Bake for 20 minutes. Pull it out and sprinkle with remaining feta cheese along with maldon salt if using. Place back in the oven and bake another 10-15 minutes until golden brown and crisp. Let the bread rest for a few minutes, remove from the pan and slice.