The oven method: 

1. Preheat the broiler to high and position a rack in the upper third of the oven. Line a baking sheet with foil and coat with cooking spray.
2. In a small bowl, make the glaze by whisking together gochujang, mirin, 1 tablespoon of tamari, honey, 1/2 teaspoon of sesame oil, 1 clove of grated garlic, and ginger.
3. Pat salmon dry and place skin-side down on the prepared baking sheet. Brush with the glaze. Broil until just cooked through, 5-8 minutes, depending on thickness.
4. Meanwhile, heat the remaining 1 teaspoon sesame oil in a large skillet over medium-low heat. Add the remaining 3 cloves garlic and cook, stirring, until fragrant and just starting to brown, about 3 minutes. Add spinach and cook until wilted. Remove from heat and stir in the remaining 1 tablespoon tamari.
5. Plate the salmon over the spinach and garnish with sesame seeds and green onions.

The sous vide method: 

1. Set up the sous vide: Preheat water to 125°F (52°C) using a sous vide machine. 
2. Make the gochujang glaze: In a small bowl, make the glaze by whisking together gochujang, mirin, 1 tablespoon of tamari, honey, 1/2 teaspoon of sesame oil, 1 clove of grated garlic, and ginger.
3. Prepare the salmon: Pat the salmon dry and brush it with the glaze. Place salmon in one large sous vide bag, leaving enough room between fillets, and vacuum seal the bag. 
4. Sous vide the salmon: Submerge the salmon in the preheated sous vide water bath and set the timer for 40 minutes. 
5. Sear the salmon: Once the timer goes off, remove the salmon from the water bath, open the bag, and gently transfer the salmon to a plate. Pat it dry. Heat a large skillet over medium-high heat. Once hot, add some oil and transfer the salmon, skin side down, into the skillet. Sear the skin for one minute and flip to sear the other side for 30 seconds. Transfer the salmon back to the plate and set aside. 
6. Round out the meal: In the same skillet, heat the remaining 1 teaspoon sesame oil over medium-low heat. Add the remaining 3 cloves of garlic and cook, stirring, until fragrant and just starting to brown for about 3 minutes. Add spinach and cook until wilted. Remove from heat and stir in the remaining 1 tablespoon tamari. Plate the salmon over the spinach and garnish with sesame seeds and green onions. Enjoy!