Preheat the oven to 300℉. Lightly spray a 9x13 pan with oil and set aside.
Remove 2 oz of the boxed cake mix and set aside. In the bowl of a stand mixer, combine the remaining 13 oz of cake mix, 1 egg, and canola oil. Mix on a low speed until evenly moistened and combined. Scrape the bowl down as needed. The mixture will be lumpy and there will be some crumbly bits.
Press the mixture into the bottom and up the sides of the prepared pan. Make sure it is an even layer. Use a flat bottomed glass to help press it down. Set aside.
In the same stand mixer bowl (no need to clean it), add the cream cheese and beat on med/ med-low speed until smooth and creamy. Scrape the bowl down as needed. This will take about 3 minutes, give or take.
Scrape the bowl down. With the mixer on a low speed, slowly drizzle in the can of sweetened condensed milk. Beat on a low/ med-low speed until smooth. Scrape the bowl down.
Add the remaining 3 eggs one at a time, mixing on a low/ med-low speed. Scrape the bowl down as needed.
Add the reserved 2 oz of cake mix and beat on a med- low speed for one minute.
Add the guava puree, lemon juice, and vanilla. Beat on low just until combined.
Pour the guava cheesecake filling into the prepared crust. Bake for 45 minutes. Turn off the oven and crack the door open for 10- 15 minutes. Remove the cheesecake from the oven and cool to room temperature, about 2 hours. Then chill uncovered for 2 hours before covering the dish with foil and chilling for several more hours, or preferably overnight.