Prepare the cucumbers. After the cucumbers are washed and dried, cut them into ¼ to ½ inch rounds and place them in a mixing bowl. Sprinkle them with the salt and gently mix. Let them sit for 20 minutes. Pour the salted cucumbers into a strainer and drain and rinse them with cold water. Dry them with paper towels and place them in a new mixing bowl. Set aside.
Prepare the vinegar and marinate. In a small sauté pan, over low heat, warm the sugar with the vinegar only until it dissolves, about 2 minutes. Pour this over the cucumbers and gently mix. Cover the bowl with plastic wrap and let them marinate in the refrigerator for at least 2 hours. Stir them once or twice during this time.
Make chili oil. In a small sauté pan, heat the grapeseed oil with the sesame oil and chili paste. Cook only until it's sizzling, about 2 minutes. Stir and let it cool to room temperature.
Add the chili oil, marinate and serve. Remove the cucumbers from the refrigerator. Stir in the chili oil and return them to the refrigerator for at least 2 hours and ideally overnight to continue to marinate.