Spray an extra large lasagna or other baking dish with non-stick oil, and chop the sour dough bread into cubes. Set aside.
Heat the extra virgin olive oil over in a medium size pan over medium heat.
Add the onions and peppers and sauté until the colors are vibrant (about 4 minutes).
Next add the garlic and the vegan ground sausage. Sauté until cooked through.
Remove from heat and mix in the mustard and spinach.
In a medium bowl, whisk together all of the ingredients for the vegan egg until smooth.
Layer the bread cubes, vegan sausage mixture, vegan egg and Daiya cheese into the baking dish. Cover with tin foil and chill in the refrigerator overnight.
When ready, place the casserole in the oven at 350°F for 1 hour. (I wouldn't make this more than 1-2 days in advance).
Enjoy!