Heat a large oven-safe skillet over medium-low heat and add the butter. Add in the onions with a pinch of salt and pepper and stir. Cook, stirring often, until the onions caramelize, about 30 to 40 minutes. Once the onions are golden and caramelly, transfer them to a plate.
Add the olive oil to the same skillet and toss in the spinach and garlic. Stir, cooking until the spinach wilts. Stir in the chicken and a pinch of salt and pepper. Transfer the mixture a separate plate from the onions.
(At this point, you can boil a pot of salted water and cook the lasagna noodles until they are al dente. Once they are finished, lay them out on a clean towel. Don’t let them stick together! )
Preheat the oven to 350 degrees F. In a bowl, stir together the ricotta, parmesan, egg, salt and pepper.
Assemble your roll ups! Lay all the lasagna noodles out in a single layer. Spread a spoonful or two of the ricotta on all the noodles. I would do all the ricotta first, so you can spread any extra on the noodles. Top the ricotta with the spinach and chicken mixture on each noodle. Then go through and top each with the caramelized onions. Sprinkle the roll ups with the gruyere cheese, keeping some to sprinkle on top of the noodles.
To make the bechamel, heat the same skillet to medium heat. Add the butter and once melted, whisk in the flour to create a roux. Cook the roux for 2 to 3 minutes until it smells nutty and fragrant. Slowly stream in the milk while whisking constantly until it’s smooth. Once smooth, add in the thyme, nutmeg and a pinch of salt and pepper.
Roll up each lasagna noodle and place it right in the bechamel with the seam side down. Repeat with the remaining noodles and then spoon the bechamel over all the noodles. Top with the remaining gruyere cheese.
Bake for 30 minutes, or until golden and bubbly. Garnish with fresh thyme and chives. Serve immediately.