Rhubarb Upside Down Cake

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Nonstick cooking spray, for the pan

6 cups rhubarb sliced on the bias about 1 1/2-inches thick

3/4 cup sugar 

1/4 cup honey 

1 tablespoon lemon juice 

2 teaspoons fresh thyme leaves 

1/2 teaspoon ground cinnamon 

1/2 teaspoon ground ginger 

1/4 teaspoon salt 

1 teaspoon vanilla bean paste 

1 box yellow cake mix 

Whipped cream, lightly sweetened with vanilla bean paste, for serving (optional)