Megalomaniak
Attached the godot project:
var surface_array = []
surface_array.resize(Mesh.ARRAY_MAX)
var vertices = PackedVector3Array()
var uvcoords = PackedVector2Array()
var indices = PackedInt32Array()
vertices.push_back(Vector3(-0.2, 1, 0))
vertices.push_back(Vector3(0.2, 1, 0))
vertices.push_back(Vector3(1,-1,0))
vertices.push_back(Vector3(-1,-1,0))
uvcoords.push_back(Vector2(0,0))
uvcoords.push_back(Vector2(1,0))
uvcoords.push_back(Vector2(1,1))
uvcoords.push_back(Vector2(0,1))
indices.push_back(0)
indices.push_back(1)
indices.push_back(2)
indices.push_back(0)
indices.push_back(2)
indices.push_back(3)
surface_array[Mesh.ARRAY_VERTEX] = vertices
surface_array[Mesh.ARRAY_TEX_UV] = uvcoords
surface_array[Mesh.ARRAY_INDEX] = indices
var mesh = ArrayMesh.new()
#mesh.blend_shape_mode = Mesh.BLEND_SHAPE_MODE_NORMALIZED
mesh.blend_shape_mode = Mesh.BLEND_SHAPE_MODE_RELATIVE
mesh.add_surface_from_arrays(Mesh.PRIMITIVE_TRIANGLES, surface_array)
$mesh_instance.mesh = mesh