Cook the spinach according to package directions (6-8 mins in microwave). Cool and drain, squeezing out excess water. Season with salt and pepper.
Boil pasta according to package directions in salted water.
In the bottom of a pie plate drizzle some olive oil, next add all of the spinach, spread out into a thin layer. Add salt and fresh black pepper, garlic (I like to grate mine on microplane so can be evenly distributed) and the juice of half of the lemon.
Place half of the spaghetti on top. Drizzle with olive oil. Layer half of the swiss cheese, breaking it into strips, and half of the tarragon.
Add the second half of spaghetti, some more olive oil, juice of the second half of the lemon, parmesean cheese, second half of swiss, and second half of tarragon.
Bake uncovered at 400 degrees for 20 minutes.
Allow to rest for 5 minutes to allow for easier slicing into wedges.