There is so much you can do with slimy spinach. One favorite of mine is to put it into smoothies. You can't taste it and it is an easy way to get more greens. Not an appetizing color however. Rinsing the spinach will take away some of the slime/bitterness.
1 c. apple juice
1/2 c. frozen strawberries
1/2 c. frozen peaches
handful of spinach
1/2-1 c. ice depending on desired thickness
Add to blender in order and blend. Drink with a straw. :)
Often I substitute the strawberries and peaches with 1 c. frozen Dole mixed fruit from Sam's.