Cook the onion and bell pepper in the olive oil in a saucepan over low heat, stirring, until soft, about 10 minutes.
Add the ham and cook, stirring, 10 more minutes.
Add the butter and let melt, then add the smoked paprika and flour and cook, stirring, about 5 minutes.
Whisk in 1 3/4 cups milk and bring to a simmer. Cook, stirring, until thick, 5 to 7 minutes. Season with salt and pepper.
Remove from the heat and stir in the manchego until melted.
Scatter the gelatin over the remaining 1/4 cup milk in a bowl and set aside, 5 minutes.
Whisk the gelatin mixture until smooth, then stir into the cheese mixture.
Transfer to a shallow baking dish and refrigerate until firm, about 1 hour.
Line a baking sheet with parchment paper. Put some flour in a shallow bowl. Beat the eggs in another bowl and put the breadcrumbs in a third bowl. Scoop out about 1 tablespoon of the cheese mixture and form into a football shape. Dredge in the flour, then dip in the eggs and roll in the breadcrumbs.
Transfer to the prepared baking sheet. Repeat to make about 40 croquetas. Refrigerate until ready to fry.
Heat about 2 inches of canola oil in a deep skillet over medium-high heat until a deep-fry thermometer registers 360 degrees F. Working in batches, fry the croquetas until golden brown, about 2 minutes.
Remove with a slotted spoon and drain on paper towels. Season with salt.
