Grilled Fresh Portabello Mushroom and Spinach Sandwich

I like those big meaty portabella mushrooms.
They tend to dry out on the grill and also
tend to turn all wet and mushy in the oven.
Here is a recipe to solve both problems.
These burgers go wonderfully with a tossed
green salad and balsamic vinaigrette dressing.

Ingredients:
4 large Portabello mushroom heads (caps)
Whole grain bread or crusty sandwich rolls
2 teaspoons extra virgin olive oil
Baby spinach leaves

Ingredients:
For Basil-Lemon Pesto Sauce:
2 cups loosely packed fresh basil leaves
1 teaspoon fresh lemon juice
2 cloves garlic, finely chopped
Sea salt, to taste
2 tablespoons extra-virgin olive oil

Directions:
To make the tangy basil-lemon pesto,
combine basil, garlic, and salt in a food processor
or blender and process until finely chopped.
Add extra virgin olive oil and lemon juice,
then process again until smooth.
If you don't use all of it up with the burgers,
you can keep any remaining sauce
in an air-tight container
in the refrigerator for up to 2 days.

To make the Portabello burgers:
Brush each mushroom on rounded underside
and rim with about half a
teaspoon of extra-virgin olive oil,
then season with sea salt.
Place the mushroom heads, gill sides down,
on grill over medium-high heat. Grill for 3 minutes.
Turn mushroom heads over and grill for another 3 to 4 minutes,
rotating each mushroom about half a turn after 2 minutes;
the goal is to have the bottoms brown nicely.
Place a grilled mushroom, gill side up,
on the bottom half of your whole
grain sandwich bread or roll.
Fill each cap with about 3-4 teaspoons
of the basil-lemon pesto,
then finish by topping with baby spinach leaves.
Close each roll and enjoy while they're hot!